When do the FASTIN patents expire, and when will generic FASTIN be available?

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Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Exclusivity Expiration
Glaxosmithkline	FASTIN	phentermine hydrochloride	CAPSULE;ORAL	017352-001	Approved Prior to Jan 1, 1982		DISCN	No	No	⤷ Start Trial	⤷ Start Trial				⤷ Start Trial
>Applicant	>Tradename	>Generic Name	>Dosage	>NDA	>Approval Date	>TE	>Type	>RLD	>RS	>Patent No.	>Patent Expiration	>Product	>Substance	>Delist Req.	>Exclusivity Expiration

Last updated: July 22, 2026

FASTIN (phentermine) Investment Scenario and Patent/Exclusivity Fundamentals Analysis for 2026

Fastin is the U.S. brand of phentermine, an old, small-molecule weight-loss agent. From an investment and IP-readiness standpoint, the opportunity set is dominated by (1) regulatory-admin exclusivity that is essentially exhausted, (2) a market structure shaped by generics and contract manufacturing, and (3) limited ability to create new exclusivity unless a company owns differentiated reformulations or method-of-use IP that can withstand generic design-around.

Because “FASTIN” is widely available as generic phentermine in the U.S., the core investor question is not “How long does exclusivity last?” but “Is there any credible, protectable differentiation in an owned product (dose form, release profile, combo, or indication scope), or is the economics purely competitive/price-led?”

What is Fastin (phentermine) and what products compete with it in the U.S.?

Fastin is marketed as a sympathomimetic amine anorectic for short-term management of exogenous obesity as part of a weight-loss regimen. The drug is typically sold as immediate-release oral capsules/tablets depending on the historical label presentation.

What formulation and strength risks matter for investors

Phentermine is not a biologic and has no platform-type IP typical of monoclonal antibodies. For investor fundamentals, the key risk factors are:

Generic entry is routine because the active is off-patent in practical terms.
Manufacturing is commodity-like once generic approvals are in place.
Label-driven competition is intense if multiple ANDA manufacturers sell the same dose forms.

Which competitive categories shape price

ANDA generics of phentermine (primary)
OTC/adjacent weight-loss brands (substitutes, not direct IP threats)
Newer obesity class drugs (GLP-1, dual agonists). They compete for treatment dollars even when they are not direct substitutes in the same regimen logic.

What is the Orange Book status of Fastin (phentermine)?

Orange Book exclusivity and patent coverage for Fastin is not the central value driver in the U.S. market because phentermine is an established drug with long-expired composition-of-matter and most “classic” patent coverage. The practical investor impact is that entry barriers are low for generic phentermine products.

How to think about Orange Book listings for a legacy weight-loss molecule

For a drug like phentermine, investors should treat Orange Book items as:

Potentially surviving formulation patents (if any are listed)
Method-of-use claims (rare for a first-line, label-limited appetite suppressant where label history is long)
Manufacturing process claims (usually easier to design around or avoid in generic scale-up)

In practice, for legacy phentermine brands, the listings do not usually prevent generic availability.

When does Fastin lose exclusivity and what does that imply for generic launch timing?

For phentermine/old-brand settings, the exclusivity answer for U.S. product-level investors is: exclusivity has effectively run out for composition and most typical exclusivity categories. The implication is:

Generic availability is already priced into the market.
Any incremental “launch” is more often about distribution, contracts, and supply chain, not a new IP horizon.

What “launch timing” actually looks like

In a matured generic environment, “timing” is:

When supply disruptions end
When contract bidding cycles reward lower acquisition costs
When competitors adjust pricing due to new ANDA supply

Not when a patent barrier falls.

What patents protect phentermine (Fastin) and how strong is the patent estate?

A high-level investment assessment for phentermine-based brands is:

Composition-of-matter estate is not a durable moat.
Any remaining IP, if present, is most likely in limited formulation or manufacturing claims.
Method-of-use protection is constrained by historical label scope and the age of the active ingredient.

Patent strength scorecard for legacy small molecules

For an investor, the practical “strength” dimensions are:

Can a generic avoid the claim by changing excipients, process, or physical form?
Can a potential entrant design around without losing bioequivalence?
How many additional Orange Book patents are listed, and are they enforceable on relevant products?

For Fastin/phentermine, the market structure indicates this estate has not prevented broad generic commercialization.

What generic entry risks exist for Fastin (phentermine) in the U.S.?

Generic entry risk for Fastin is largely historical and structural rather than a near-term catalyst:

If generics already cover the drug, the main risk is price erosion and margin compression from additional supply.
If a brand has a niche advantage (specific dosage strength, contract placement, or supply reliability), that advantage can still erode as new supply enters.

Where a brand can still lose economics even without “new” legal entry

Even after all major generics exist, incremental entry can happen via:

Additional ANDA manufacturers with lower cost structures
Larger-scale contract manufacturing shifting supply economics
Distributor switching due to rebate economics

What formulations are protected for Fastin and do they matter commercially?

Commercial differentiation in phentermine is typically limited. For investors, the only “formulation matters” scenario is when there is a credible, enforceable patent protecting:

A specific dose form (capsule vs tablet)
A specific release profile (rare for phentermine label history)
A specific excipient/solid-state profile with real PK advantage

Investment read-through

If no clearly differentiated, enforceable formulation IP exists, then Fastin’s commercial economics are dominated by:

Pharmacy benefits manager (PBM) contracting and rebates
Wholesale acquisition cost (WAC) and distributor terms
Supply continuity and manufacturing cost

How do Fastin economics compare with newer obesity drugs that compete for prescriptions?

Even if phentermine remains prescribed for short-term obesity management, the competitive landscape is structurally altered by:

GLP-1 receptor agonists and dual agonists capturing a share of chronic weight management
Higher willingness-to-pay segments in insured populations that favor advanced therapies

Investor implication

Phentermine/fastin category growth depends less on IP and more on:

Reimbursement and access
Physician preference for low-cost short-term options
Treatment setting (primary care vs specialty weight management)

What companies are selling Fastin or generic phentermine in the U.S., and how does that impact margins?

This category typically features:

Multiple generic manufacturers with overlapping supply
Price competition that compresses branded-to-generic spreads

Investor fundamentals approach

Treat brand share as a function of contracting and channel strategy.
Treat profitability as a function of manufacturing cost, rebate rates, and supply reliability.
Treat downside risk as rapid price drops when wholesalers and payers re-optimize.

What patent litigation affects phentermine/weight-loss brands and could it move the stock or credit profile?

For an established commodity like phentermine, litigation is less likely to be the primary driver than it is for newer, high-value oncology or rare-disease IP.

Investment takeaway

If you are assessing equity or credit exposure, weight the probability of major patent outcomes as low unless the investor thesis is explicitly built around a live case, settlement, or newly granted formulation patents.

What FDA regulatory status applies to Fastin (phentermine) and how does it affect market access?

Fastin is an FDA-regulated prescription product under standard small-molecule rules. Regulatory considerations for investors are:

Bioequivalence and generic substitution (ANDA pathway)
Label scope stability
Manufacturing compliance (CGMP, inspections)

Key regulatory issue for commodity drugs

In matured generics, the main regulatory swing factor is manufacturing execution. This affects:

Availability and backorders
Compliance-driven supply interruptions
Margin volatility tied to production yield and scrap

How should investors model revenue exposure for Fastin in a mature generic category?

Revenue modeling should be anchored on:

Total market demand for short-term obesity pharmacotherapy
Share of prescriptions relative to competing weight-loss therapies
Net price after rebates and payer concessions

Business model reality

For a mature drug:

Growth is typically modest
Volatility is driven by pricing, reimbursement changes, and manufacturing/supply events
IP-driven upside is limited unless the company owns a differentiated pipeline beyond the legacy brand

What are the best-case and base-case investment scenarios for Fastin?

Base-case (most consistent with commodity realities)

Market stays competitive
Brand pricing remains constrained by generic anchors
Growth is steady but limited
Profitability improves via cost control and contracting, not through IP

Best-case (credible only with differentiation)

A company owns enforceable, commercially material formulation/process/method-of-use IP that delays meaningful substitution for a specific product configuration
Or a company has strong distribution advantage that sustains net pricing above the generic floor
Or a company has a complementary branded portfolio that stabilizes margins

Key takeaways for investors evaluating Fastin fundamentals

IP is not the moat for Fastin/phentermine in the U.S.; the asset behaves like a mature commodity in a generic market.
The investment question shifts from exclusivity to contracting, net price, manufacturing execution, and supply continuity.
Competitive pressure comes from generic phentermine and substitution by newer obesity drugs, affecting demand and payer behavior.
Any meaningful upside requires real product differentiation (legally protectable) or channel economics rather than patent-driven timing.

FAQs

1) Is Fastin still prescribed and reimbursed in the U.S.

Yes, but utilization is increasingly sensitive to payer rules, rebate dynamics, and competition from newer obesity therapies.

2) Can a new generic manufacturer enter phentermine easily in the U.S.

The pathway is well established; entry risk is structural, driven by pricing rather than waiting on patent expiration.

3) What drug class does Fastin belong to and why does it matter for competition

Fastin is a sympathomimetic appetite suppressant; it competes within obesity pharmacotherapy where GLP-1 and dual agonists set treatment expectations and payer preferences.

4) Are formulation patents a realistic lever for protecting phentermine profits

Only if a company holds specific, enforceable IP tied to clinically and commercially meaningful differentiation; otherwise, differentiation is limited and design-around is typical.

5) What operational risks are most material for a phentermine brand

Manufacturing compliance, supply availability, and cost of goods are the dominant drivers of near-term profitability in commodity categories.

References

FDA. “Orange Book: Approved Drug Products with Therapeutic Equivalence Evaluations.” U.S. Food and Drug Administration.
FDA. “ANDA (Abbreviated New Drug Application) Pathway.” U.S. Food and Drug Administration.
FDA. “Drug Approval and Development: Generic Drug Development.” U.S. Food and Drug Administration.

US Patents:	0
Applicants:	1
NDAs:	1

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