Second or subsequent offenses. a. Any person convicted of any offense under this act, if the offense is a second or subsequent offense, shall be punished by a term of imprisonment of up to twice that otherwise authorized, by up to twice the fine otherwise authorized, or by both.
b. For purposes of this section, an offense shall be considered a second or subsequent offense, if, prior to the commission of the offense, the offender has at any time been convicted of an offense or offenses under this act or under any law of the United States or of any state relating to narcotic drugs, marihuana, depressant, stimulant, or hallucinogenic drugs.