GHB and speed/amphetamine
Speed is sometimes combined with GHB to take the edge off speed or to get hornier when used in a sexual setting. The risk of this is that due to the stimulating effect of speed, you will not feel the anesthetic effect of GHB properly, increasing the chance of overdosing with GHB. If you then take too much GHB, your body is still stimulated, but you are no longer or not fully conscious. This looks rather weird and intense. Someone then moves very strangely and is no longer (properly) approachable.
Here you can read more about what to do if someone passes out.
Some people think that combining speed with GHB works against passing out. You can then feel clearer than under the influence of GHB alone. But it doesn’t really stop passing out. There is also a chance that you will take more GHB than you would if you were only using GHB. There are indications that if you go into a coma due to an overdose of GHB in combination with speed, the chance of a deep and longer coma is many times greater. And the likelihood of complications during the coma is higher. So never use ‘uppers’ to prevent passing out. Only sensible dosing with GHB helps against passing out. In addition, there is an increased risk of epileptic activity in the brain and an increased risk of movement disorders (automatic movements, agitation, self-mutilation).