http://revach.net/article.php?id=3545

Section: Halacha   Category: Tshuvos
Aruch HaShulchan & Rav Vosner - Lending Money Without A Contract
The gemara (Bava Metzia 75b) says that you may not lend money without the lender giving you a shtar.  Since without one the borrower can deny the loan, you are oveir Lifnei Iveir.  The Shulchan Aruch (CM 70:1) says that you may lend without a shtar if you receive collateral which also insures against the borrower's denial.  However, it is not as preferable as a shtar.  The reason, says the Aruch HaShulchan, is because there can still be arguments as to the exact amount of the loan.

The Aruch HaShulchan further says that the reason we are not Makpid on this today and we lend without Eidim or a shtar is because we know each other and trust each other so there is no worry about forgetting or denials.  Rav Vosner (Shevet HaLevi 10:268) says that it is not worth it to rely on this Heter and you should only lend money with a shtar as required by the Shulchan Aruch.  Even the Amora'im didn't lend each other without a shtar.  Although the gemara says that they were so busy learning they needed a shtar to remind them about the loan, nevertheless says Rav Vosner, we also have our own things that we are busy with and therefore must also only lend with a shtar.

Important Note: We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. One should learn the tshuva to verify the accuracy of our interpretation.  Please also understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.