Phenylephrine is used as a decongestant, available as an oral medicine or as a nasal spray. Phenylephrine is now the most common over-the-counter (OTC) decongestant; oxymetazoline is a more common nasal spray.[citation needed] Pseudoephedrine was historically more common, although its notoriety as a methamphetamine precursor has led some governments to restrict its sale.

Phenylephrine or Neo-Synephrine is an a-adrenergic receptor agonist used primarily as a decongestant, as an agent to dilate the pupil and to increase blood pressure. Phenylephrine has recently been marketed as a substitute for pseudoephedrine, (e.g. Pfizer's Sudafed (Original Formulation)) but there are recent claims that oral phenylephrine may be no more effective as a decongestant than placebo

Oral phenylephrine is extensively metabolised by monoamine oxidase [1], an enzyme which is present in the gastrointestinal tract and the liver. Therefore, compared to orally-taken pseudoephedrine, it has a reduced and variable bioavailability of only up to 38 percent [2][3], and is therefore less effective as a nasal decongestant than pseudoephedrine. Because phenylephrine is a direct selective a-adrenergic receptor agonist, it does not cause the release of endogenous noradrenaline like pseudoephedrine does. Therefore, phenylephrine is less likely to cause side-effects like central nervous system stimulation, insomnia, anxiety, irritability and restlessness.

FDA informed healthcare professionals and patients of the possibility of severe and sometimes incapacitating bone, joint, and/or muscle (musculoskeletal) pain in patients taking bisphosphonates. Although severe musculoskeletal pain is included in the prescribing information for all bisphosphonates, the association between bisphosphonates and severe musculoskeletal pain may be overlooked by healthcare professionals, delaying diagnosis, prolonging pain and/or impairment, and necessitating the use of analgesics. The severe musculoskeletal pain may occur within days, months, or years after starting a bisphosphonates. Some patients have reported complete relief of symptoms after discontinuing the bisphosphonate, whereas others have reported slow or incomplete resolution. The risk factors for and incidence of severe musculoskeletal pain associated with bisphosphonates are unknown

Sibutramine (trade name Meridia in the USA, Reductil in Europe and other countries), usually as sibutramide hydrochloride monohydrate, is an orally administered agent for the treatment of obesity. It is a centrally-acting serotonin-norepinephrine reuptake inhibitor structurally related to amphetamines,[1] although its mechanism of action is distinct.Sibutramine is manufactured by Abbott Laboratories. It is classified as a Schedule IV controlled substance in the United States.