Astemizole
Astemizole (marketed under the brand name Hismanal, developmental code R43512) was a second-generation antihistamine drug that has a long duration of action. Astemizole was discovered by Janssen Pharmaceutica in 1977. It has been withdrawn from the market in most countries because of rare but potentially fatal side effects (QTc interval prolongation and related arrhythmias due to hERG channel blockade).
Recreational use of dextromethorphan
A formal survey of dextromethorphan users showed that more than half of users reported experience of the following withdrawal-symptoms individually for the first week after long-term/addictive dextromethorphan use: fatigue, apathy, flashbacks, and constipation. Over a quarter reported insomnia, nightmares, anhedonia, impaired memory, attention deficit and decreased libido. Rarer side effects included panic attacks, impaired learning, tremor, jaundice, urticaria (hives) and myalgia. DXM has also been "known to increase the frequency of complex partial seizures in epileptics by 25% compared to placebo." Frequent and long-term usage at high doses could possibly lead to toxic psychosis and other permanent psychological problems. It is important to note that medical DXM use has not been shown to cause the above issues.