When a Christian dies due to an overdose on drugs, do they enter heaven? 


That would be a judgment that God makes. We know that using drugs recreationally is wrong because it clouds our thinking. "But you, brethren, are not in darkness, that the day would overtake you like a thief;  for you are all sons of light and sons of day. We are not of night nor of darkness;  so then let us not sleep as others do, but let us be alert and sober.  For those who sleep do their sleeping at night, and those who get drunk get drunk at night.  But since we are of the day, let us be sober, having put on the breastplate of faith and love, and as a helmet, the hope of salvation" (I Thessalonians 5:4-8). Drunkards cannot enter heaven (I Corinthians 6:9-10), so it would be reasonable to conclude that those who are regularly high on a drug will not make it either.