Taking Suboxone regularly will likely lower your opiate tolerance. If you have been taking high doses of opioids and then you get on Suboxone treatment, over time your body’s tolerance to opioids begins to decrease and go back to normal. This is overall a good thing because it is a sign that your body is readapting after long term opioid misuse. However, if a person relapses after being on Suboxone and attempts to take the same doses of a drug like heroin or fentanyl that their body was previously used to taking, they can overestimate their tolerance and can overdose. This is one of the risks of relapse during Suboxone therapy.
Repeated drug use changes brain chemistry. In time, many people need take more opioids to get the effects that a smaller dose once delivered, or even just to prevent withdrawal symptoms. This is a phenomenon called “tolerance”.
Typically, people with an opioid use disorder have a high opioid tolerance. Doses that would kill someone who never took drugs may be routine for someone whose body is used to the effects of opioids.
When a patient starts Suboxone, which is a “partial” opioid agonist, their brain begins to heal, and their tolerance for full opioid agonists goes down after time. This process takes weeks to months or even years.  In fact, with time, you may even take smaller amounts of Suboxone until you no longer need it to prevent cravings from opioids.
If you have been in recovery for a long time on Suboxone, your brain cells are no longer accustomed to large doses of opiates. If you return to drug use, particularly if you relapse to immediately using the same doses you used previously, you could put yourself at risk for overdose. 
Sticking with your Suboxone therapy for at least 12 months is associated with lower relapse risks. In one study, of those treated for up to 18 months, about 5% needed overdose treatment within six months of quitting therapy.
Relapse is an unfortunate but common part of the recovery process. However, if you have been on Suboxone and do experience the urge to relapse, there may be additional risks, including the risk of overdose due to decreased tolerance.
If you're tempted to start misusing opiates again while on Suboxone, talk with your treatment team immediately. They can adjust your Suboxone dose and offer other forms of behavioral support and supervision to help prevent you from relapsing to opioid misuse.