Older Appetite Suppressants

What these drugs are

All three are stimulant-type appetite suppressants, taken as tablets before meals, and all three labels approve them only as a short-term addition to a calorie-restricted weight-reduction programme. The labels describe them in almost the same words: sympathomimetic amines with activity similar to the amphetamines. What separates them from each other is the dosing schedule, the controlled-substance class and the price.

They are not the same thing as the modern weight-loss medicines. Those act on gut hormones, were tested in trials running well past a year, and are approved for long-term use. These three are approved for a few weeks, and their labels carry no weight-loss figure at all.

The three drugs

What the evidence does and does not show

This is the part of the page where the honest answer is an absence. For phentermine there are three published randomised trials and a health-record study of nearly 14,000 people. For these three drugs there is no comparable published evidence to cite, so nothing on this page can tell you how much weight participants lost, how many reached 5% or 10% weight loss, or what happened after treatment stopped.

What the labels do state is the class finding, in almost identical wording on all three: the extra weight loss of drug-treated patients over placebo-treated patients is “only a fraction of a pound a week”. The phendimetrazine label adds that tolerance to the appetite-suppressing effect develops within a few weeks.

Who the labels say they are for — and who they are not for

The contraindication lists overlap, without being identical. All three rule out an overactive thyroid, glaucoma, agitated states, a history of drug abuse and known hypersensitivity to sympathomimetic amines, and all three warn that hypertensive crises may result from use during or within 14 days of a monoamine oxidase inhibitor. The phendimetrazine and benzphetamine labels add advanced arteriosclerosis, symptomatic cardiovascular disease and moderate-to-severe high blood pressure; the diethylpropion label contraindicates advanced arteriosclerosis and severe high blood pressure, and treats symptomatic cardiovascular disease as a caution rather than a bar. The diethylpropion label also lists pulmonary hypertension and rules out combining it with other appetite suppressants, and the benzphetamine label states that it is contraindicated in women who are or may become pregnant.

The 2015 Endocrine Society guideline recommends against using diethylpropion — and phentermine — in people with uncontrolled high blood pressure or a history of heart disease. Whether any of this applies to you is a question for the clinician who can see your blood pressure and your medicines list.

Side effects the labels list

These labels predate the modern format, so they group side effects by body system and give no percentages. The lists are dominated by stimulant effects.

How long they are meant to be taken

Diethylpropion. The label limits use to a few weeks and says that if tolerance develops the dose should not be increased — the drug should be stopped instead. It also sets a stopping rule for the start of treatment: to 'limit unwarranted exposure and risks', treatment 'should be continued only if the patient has satisfactory weight loss within the first 4 weeks of treatment (e.g., weight loss of at least 4 pounds, or as determined by the physician and patient)'.

Phendimetrazine. The label limits use to a few weeks and states that 'tolerance to the anorectic effect of phendimetrazine develops within a few weeks'; when that happens it says the drug should be stopped rather than the dose increased.

Benzphetamine. The label limits use to a few weeks and says that where tolerance develops the drug should be stopped rather than the dose increased. It also sets a stopping rule for the start of treatment: to 'limit unwarranted exposure and risks', treatment 'should be continued only if the patient has satisfactory weight loss within the first 4 weeks of treatment (i.e., weight loss of at least 4 pounds, or as determined by the physician and patient)'.

Unlike phentermine, these three have no large study of longer-term use to set against their labels — so on duration, the label is all the evidence there is.

What they cost

Two of the three are cheap. Diethylpropion and phendimetrazine both come in at well under a hundred dollars for a 30-day supply at cash prices, and less with a discount card. Benzphetamine is the exception, and it has no single price at all: on one day, the discount-card prices listed for the same 90-tablet bottle ran from around $122 at one pharmacy chain to nearly $870 at another, with one cash price listed above $1,500.

These are US cash prices checked on one day, and they move. A discount-card price is not an insurance price, and your pharmacy may quote something different.

How they compare in the evidence

• →Against phentermine. Same drug class, same few-weeks approval, similar price for two of the three — but phentermine has randomised trials and a large health-record study behind it, and these three do not.
• →Against the newer medicines. The drugs approved for long-term weight management were tested in trials of 68 to 72 weeks that reported percentage weight loss. No such number exists for these three, so the two cannot be set side by side.
• →Controlled-substance class. Phendimetrazine and benzphetamine are Schedule III; diethylpropion and phentermine are Schedule IV.

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Last reviewed: September 2026