Norephedrine

Norephedrine, better known as phenylpropanolamine or PPA, occupies two unrelated positions. It is a minor metabolite of amphetamine, formed by side-chain hydroxylation, and it was for decades a widely sold sympathomimetic drug in its own right, present in cold and cough remedies as a decongestant and in over-the-counter products as an appetite suppressant.

Pharmacologically it is an indirect sympathomimetic with a weaker and more peripheral profile than amphetamine, producing vasoconstriction, a rise in blood pressure and appetite suppression, with comparatively little central stimulation at ordinary doses.

Its significance now is as a safety story. The Hemorrhagic Stroke Project, a case-control study published in 2000, found phenylpropanolamine associated with haemorrhagic stroke; the association was concentrated in women, and the appetite-suppressant indication carried a notably raised risk including among first-time users ^[1]. Regulators moved to withdraw it, and subsequent work continued to examine the risk attached to the cold-remedy use as well ^[2]. It has also been identified among the modifiable risk factors for aneurysmal subarachnoid haemorrhage in young people ^[3].

The compound remains available in some jurisdictions and in veterinary medicine, but its era as a mass-market over-the-counter drug ended with that finding.

The safety profile is dominated by one finding, and it is the reason the drug is no longer in general use.

A case-control study published in 2000 found phenylpropanolamine associated with haemorrhagic stroke. The association was concentrated in women; the appetite-suppressant use carried a notably raised risk, including in first-time users, and the risk attached to the cold-remedy use was less clear but not dismissed ^[1]. Later analysis continued to examine the cold-remedy exposure specifically ^[2], and the compound was identified among modifiable risk factors for aneurysmal subarachnoid haemorrhage in young people ^[3]. Regulators moved to remove it from over-the-counter products.

The absolute risk was low, which is why decades of ordinary use produced no visible signal. That is the important part rather than a mitigating footnote: a rare, severe outcome in a young and otherwise healthy population is invisible to routine pharmacovigilance and only becomes detectable when someone designs a study to look for it.

The ordinary effects at ordinary doses are those of a peripheral sympathomimetic: raised blood pressure, headache, restlessness and insomnia. Anyone with hypertension, cerebrovascular disease or a known aneurysm has an obvious reason to avoid it, and combining it with monoamine oxidase inhibitors is a route to hypertensive crisis. It is not something to seek out, and this entry is educational rather than medical advice.

Phenylpropanolamine entered wide use in the mid-twentieth century as a decongestant and became one of the most commonly consumed drugs in the United States, present in a large number of cold and cough preparations. From the 1970s it was also sold over the counter as an appetite suppressant, which is the use that eventually determined its fate.

Concern accumulated slowly through case reports of haemorrhagic stroke in young women, but case reports cannot establish an association for a rare outcome in a heavily exposed population. The question was settled by the Hemorrhagic Stroke Project, a case-control study published in the New England Journal of Medicine in 2000, which found an association concentrated in women, with the appetite-suppressant indication carrying a raised risk that included first-time users ^[1].

Regulatory action followed quickly, and phenylpropanolamine was removed from over-the-counter products in the United States. Analysis of the risk attached to the cold-remedy exposure continued afterwards ^[2], and the compound was subsequently listed among modifiable risk factors for aneurysmal subarachnoid haemorrhage in young people ^[3]. It survives in some jurisdictions and in veterinary medicine, where it is used for urinary incontinence in dogs.

Phenylpropanolamine's reputation is now almost entirely a regulatory one. It is cited routinely as the case study for why long, uneventful over-the-counter use is weak evidence of safety: it was cheap, ordinary and enormously widely taken, and none of that surfaced a rare severe outcome until a study was designed specifically to look ^[1].

Among people interested in stimulants it is remembered chiefly as the thing diet pills used to contain, and occasionally as a curiosity from a period when a sympathomimetic could be sold beside the cough syrup. That memory is accurate and tends to understate how ordinary it was.

In pharmacology it is also known as an amphetamine metabolite, which is the connection most readers arrive at this entry through, and it is a genuinely minor one; it contributes little to what amphetamine does, and the drug's own history is far more interesting than its role as a metabolite.

It retains an unglamorous ongoing life in veterinary medicine for urinary incontinence in dogs, which is where most current prescriptions for it are written.