Like other medicines, naloxone can cause side effects in some individuals. Side effects reported include:
feeling or being sick
tremors
sweating
over-breathing (associated with an abrupt return to consciousness)
fast heart beat or disturbed heart rhythm
increased or decreased blood pressure
fluid on the lungs
fits
However, because you normally give naloxone to an individual you believe is facing an imminent fatal opiate overdose, such risks of side effects are largely irrelevant in the decision on whether to use it or not. Reducing unnecessary side effects and discomfort, through careful, graduated, use of naloxone according to the instructions for the particular product, is likely to be part of the advice and training you provide. Such careful use may also have the benefit of limiting the unpleasant withdrawals the heroin or opioid user may feel as they come round. Another important but uncommon side effect, is the risk of triggering cardiac problems in susceptible people, which in some cases could be fatal, particularly if a person receives high doses of naloxone quickly, But given that you intend to give naloxone to someone already facing the risk of a fatal overdose, the small risk of triggering such a serious cardiac problem is not a reason to avoid its use. The advice on using naloxone for overdose already addresses its careful use to try to mitigate such risks. Clinical guidelines recommend starting with a sufficient but relatively small dose of naloxone, providing further small doses as needed. Taking this graduated approach to giving the naloxone, in simple steps, will be an important element of any locally-provided information materials and training.