getdate() error in function

I have the below function which errors out telling me "Invalid use of 'getdate' within a function." I can run it as sql but not as a function, is there an issue with using getdate() in a function?

SET QUOTED_IDENTIFIER ON
GO
SET ANSI_NULLS ON
GO




ALTER function fnGetQuantity( @orderid int )
returns int
as
/************************************************** ****************************
** File: fnGetQuantity.sql
** Name: fnGetQuantity
** Desc: Used to calculate the total order quantity for an order
** Quantity is sigfrequency.timesperday * sigdosageamt.descr * orders.duration
**
** Return values: Quantity
**
** Called by:
**
** Parameters: order Id
** Input Output
** ---------- -----------
** @patientid
** Auth: DHoefgen
** Date: 04/30/05
************************************************** *****************************
** Change History
************************************************** *****************************
** Date: Author: Description:
** -------- -------- ------------------------------------------
** 05/02/05 KKowert Changed sql for effdt and added duration and
** times per day logic for zeros.
************************************************** *****************************/
begin
declare @QuantityTotal int


SELECT @QuantityTotal = (o.Duration * f.TimesPerDay * d.Descr)
FROM Orders o INNER JOIN
SIGFrequency f ON o.FreqID = f.FreqID INNER JOIN
SIGDosageAmt d ON o.DosageAmtID = d.DosageAmtID
WHERE (o.OrderID = @orderid) AND (f.Effdt =
(SELECT MAX(f2.Effdt)
FROM SIGFrequency f2
WHERE f2.FreqID = f.FreqID AND f2.Effdt <= getdate())) AND (d.Effdt =
(SELECT MAX(d2.Effdt)
FROM SIGDosageAmt d2
WHERE d2.DosageAmtID = d.DosageAmtID AND d2.Effdt <= getdate()))


return @QuantityTotal

end




GO
SET QUOTED_IDENTIFIER OFF
GO
SET ANSI_NULLS ON
GO

You can't have non-determinstic system function in a function.

Search for "Create function" in books online to see list of other functions not allowed in a function definition.

pass the getdate as parameter

create function dbo.previousday (@mydate datetime)
returns datetime
as
begin
return @mydate-1
end
go
select dbo.previousday (getdate())