Ecstasy

The XTC situation 2

2. More serotonin is released than usual. That is because ecstasy alters the shape of the reuptake proteins, causing them to change direction, as it were. Instead of guiding serotonin from the synapse back into the axon terminal, they send it from the axon terminal to the synapse.

Both processes result in excess accumulation of serotonin in the synaptic cleft, causing more signals than usual to be transmitted.