There have been a couple studies looking into this. Currently I don't think any have found any evidence to support the use of these inhalants yet.
Study in 2014
This one used 25 college-aged males with at least 3 years of resistance training at a weight of 85% of their 1RM. These subjects were instructed to not workout 48 hours before the testing sessions, and had 48-96 hours of rest between the two testing sessions to ensure they had recovered completely. They used Vick's VapoRub as a placebo.
"The results of this study indicate
no significant differences in the AI testing sessions compared to the VVR sessions"
Study in 2015
This one used 10 males, 10 females. All had 2+ years of resistance training. This one tested 1RM 72 hours apart from each other. First Baseline, the remaining two used water and Ammonia at random so neither the researcher or lifter "knew" which was being inhaled.
This study did mention many factors that could have impacted the results of this study.
- Finals weeks stress/lack of sleep.
- Concentration of ammonia might not have been potent enough. They used travel size shampoo bottles with the slits in the top. They mention that the lids might have limited the subjects from getting full exposure to the ammonia capsule.
- Timing of the lift. They say some subjects took longer to be in their desired heightened state, and they standardized the lifts at 20 seconds after the hit.
"Within the limits of this study, there was no ergogenic effect of
ammonia inhalation on dead-lift performance in recreational male and female
As a conclusion to the 2015 study it says:
"Given these findings,
if athletes and/or coaches feel that ammonia inhalants have a psychological benefit for
their programs, there is no basis to encourage or discourage their usage if their athlete has
no prior medical issues or history similar to that which was screening in this study"