Over 300 people in the Shannonside region were treated for heroin addiction last year.
It's a slight increase on the previous year.
Opioid substitution treatment is where a controlled drug, like methadone, is prescribed in place of the drug the person has become addicted to.
According to details released under the Freedom of Information Act by the HSE, 302 people in the Shannonside region got opioid substitution prescriptions under the medical card scheme last year.
There were 22 in Roscommon - seven women and 15 men.
There were 251 in Longford-Westmeath - 82 women and 169 men.
In Leitrim, Sligo and west Cavan, there were 29 - 10 women and 19 men.
Nationally, 7,290 people were given opioid substitution treatment, under the medical card scheme, last year - up 96 from the previous year.
