Naltrexone is a medication which blocks the effects of heroin and other opiate-type drugs. Its considerable potential in helping to prevent post-detoxification relapse has not been realised because patients generally refuse to take it or quickly discontinue.
However, these limitations apply to the oral formulation which has be taken daily. Longer-lasting formulations in the form of a depot injection or an implant inserted under the skin avoid the need to take the medication daily. This is the first randomised trial of an implant whose opiate-blocking effects last for about six months.