Is it obligatory to return the money to merchants and customers when repenting from selling Tramadol, given the difficulty of reaching them and the fear of scandal?

It is apparent that the questioner, the merchant, and the buyers are dealing with this property in an unlawful manner and for a prohibited purpose. The ruling on this sale is the same as the ruling on trading in prohibited items. Therefore, the seller is not obliged to return the price after receiving the unlawful compensation, nor is the buyer required to pay the remaining portion of the price to the seller; rather, he must donate it as charity. Accordingly, the questioner is not obliged to return the mentioned difference to the customers, nor to return the price of the two boxes to the merchant, but should donate whatever remains of this money as charity.