Subject Selection Criteria Rationale Route of administration. Participants are required to have used MA by the IV or smoked route to avoid exposing participants to drugs by routes of administration that produce more intensive interoceptive effects than usually used by the participants. Prior experience with smoked MA is allowed (rather than restricting the population to those with experience with IV MA) because smoked MA reaches brain sites of action as rapidly as does intravenously administered MA and smoked MA produces effects that are comparable to IV MA. Speed of administration (and rate of delivery to brain) of stimulant drugs likely impacts subjective and cardiovascular effects, so smoked and intravenously administered MA produce similar subjective effects (22-26).