Can I take a personal loan from a friend if no interest is involved?

Yes — an interest-free personal loan between friends or family, where the borrower repays exactly what was borrowed with no stipulated extra amount, is not only permissible but is described in Islamic tradition as qard hasan (a "goodly loan"), a virtuous and encouraged act of mutual support rather than a commercial transaction.

The one condition that matters: no benefit or increase can be agreed upon or expected as a condition of the loan — jurists apply the well-known fiqh maxim that "every loan that draws a [stipulated] benefit is riba," which would apply even to something informal like a friend agreeing to lend money only if repaid with a favor, discount, or larger sum. If the borrower, entirely on their own initiative afterward and without any prior agreement or expectation, chooses to repay a bit more or give a gift out of gratitude, that's a separate matter and is fine (the Prophet ﷺ himself is reported to have repaid a borrowed animal with a better one) — the line is whether it was stipulated or expected versus a genuine, voluntary, after-the-fact gesture.

Source: general Sunni fiqh on qard hasan; the jurists' maxim "kullu qardin jarra naf'an fahuwa riba" ("every loan that draws a benefit is riba") — a widely cited fiqh principle rather than a directly worded hadith.